[RFI] Keyboard RFI

[Jim Brown]

On 8/22/2013 2:58 PM, Charlie Gallo wrote:
> Well, there was some arcing at the ground block in the past, so I lifted the coax to slip on the ferrites, and the voltage is still there, but the current is low enough the ground takes care of it - ground clamp was a bit loose to, cleaned and tightened that

In normal (non-fault) operation, grounds should NEVER carry AC currents 
greater than a few mA. Likewise, the voltage between grounded objects or 
conductors should NEVER be greater than a volt or so. If there is 
voltage or current greater than these values, SOMETHING IS SERIOUSLY 
WRONG.  The legal limit for leakage current (current on the green wire) 
in a branch circuit is 6 mA.

Always consider at least these four possibilities, and test to make sure 
that none exist.

1) An AC outlet may be wired with conductors reversed.

2) The equipment connected to the remote cable (in this case, the CATV 
cable) has a serious AC fault condition (perhaps that mis-wiring 
problem, or a very major grounding or bonding error).

3) Your equipment may be defective or have a fault condition.

4) There may be a problem (fault or mis-wire) in the mains power system 
supplying you or that remote equipment.

One of the most important pieces of equipment we should all own is a 
clamp-on AC ammeter that can be set to read small AC currents. This 
generally requires a low current scale where the top of the scale is no 
more than about 5A, and a 1A scale is better.

To use a clamp-on ammeter, we must be able to clamp it around a single 
conductor. Inside the breaker panel, that's fairly easy, but to measure 
current anywhere else (like at an outlet), we need a simple breakout 
cable. I have made breakout cables by cutting away a foot or so the 
outer jacket of a short AC extension cable, exposing the individual 
conductors. I plug the cable into the outlet and the equipment into the 
other end of the cable.

73, Jim K9YC